In a wireless ad-hoc network, nodes (e.g., wireless telecommunications terminals, etc.) communicate with each other via a mesh topology without a central access point or server. The term ad-hoc reflects the fact that nodes can form networks “on the fly” without any supporting networking infrastructure, as well as the fact that the mobility of nodes can result in frequent changes in network membership and topology.
FIG. 1 depicts the salient elements of illustrative ad-hoc wireless network 100 in accordance with the prior art. As shown in FIG. 1, wireless network 100 comprises nodes 101-1 through 101-N, where N is an integer greater than one, and gateway 102, with wireless communication links between these elements indicated by “lightning bolts.” Nodes 101-1 through 101-N are capable of transmitting and receiving messages in point-to-point fashion via the wireless communication links, either between two nodes 101-i and 101-j, or between a node 101-i and gateway 102.
Gateway 102 is capable of receiving messages that originate from outside of wireless network 100, and of transmitting these messages to one or more of nodes 101-1 through 101-N. Gateway 102 is also capable of receiving messages that originate from any of nodes 101-1 through 101-N, and of transmitting these messages to one or more destinations outside of wireless network 100. As will be appreciated by those skilled in the art, gateway 102 is an unnecessary element of network 100 when nodes 101-1 through 101-N communicate only among themselves.
Nodes 101-1 through 101-N and gateway 102 typically communicate via any of a variety of wireless communications protocols, such as one of the Institute of Electrical and Electronics Engineers (IEEE) 802.11 family of protocols in ad-hoc mode (as opposed to the more-common infrastructure mode), the Bluetooth short-range wireless protocol, etc.
When nodes 101-1 through 101-N and gateway 102 are capable of transmitting and receiving messages via a path comprising two or more wireless communication links (or “hops”), network 100 is said to be a multi-hop ad-hoc wireless network. In a multi-hop ad-hoc wireless network, a routing protocol guides the delivery of messages throughout the network.
Routing protocols can generally be classified into two categories: proactive, and reactive. Proactive routing protocols, such as Destination-Sequenced Distance-Vector (DSDV) routing, try to maintain correct routing information at all nodes in the network at all times. Proactive protocols are typically table-driven, with topology changes handled through periodic broadcast of routing table updates.
In contrast, reactive (or on-demand) routing protocols, such as Ad-hoc On-Demand Distance Vector (AODV) routing, Optimized Link State Routing (OLSR), and Dynamic Source Routing (DSR), obtain a route only when needed. Reactive routing protocols typically can support rapid rates of node mobility and frequent topology changes, but suffer from a larger route-setup overhead than proactive routing protocols. Proactive routing protocols, meanwhile, are either slow to respond to dynamism in the network, or require significant bandwidth overhead to maintain up-to-date routes.
Multi-hop wireless ad-hoc networks are advantageous in that they typically cost less to deploy and maintain than other types of networks, as they eliminate the need for access points or servers, and require little or no configuration. Moreover, multi-hop wireless ad-hoc networks are an attractive candidate for Voice over Internet Protocol (VoIP) telephony because they enable mobility and can reduce wiring costs in buildings.
A disadvantage of multi-hop wireless ad-hoc networks, however, is that they can be difficult to “scale up” to large numbers of nodes. Consequently, multi-hop ad-hoc wireless networks are typically most attractive for deployment in small and medium-size enterprises.